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Computer science AS level theory > Communication (Chapter 2) > Flashcards

Communication (Chapter 2) Flashcards

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1
Q

How is a wireless network set up ?

A

Since there are no wires, devices called Wireless Access Points (WAPs) are used. Several of them are placed in fixed locations to permit uninterrupted wireless connection.

The WAP is a hardware component that is usually a part of the router and provides radio communication from the central device to the nodes on the network and vice versa.

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2
Q

What is a Wireless Access Point (WAP) ?

A

The WAP is a hardware component that is usually a part of the router and provides radio communication from the central device to the nodes on the network and vice versa.

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3
Q

What are the differences between a wired network and a wireless network ?

A
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4
Q

What is a client-server model ?

A

In the client-server model, there are clients (computers) which communicate with a central server (a computer could act as the server).

Files are saved on servers
Clients send requests to the servers
The servers process the requests and return the results to the client
The client displays the results to the user

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5
Q

When are client-server models used ?

A

A client-server model is used when,

  • There is a large user base
  • The access to the network resources needs to be controlled
  • There is a need for good security
  • The data has to be secure and backed up

Examples of client-server models are : -

A star network
A print server
A file server
A bank
Sending and receiving emails

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6
Q

What are the pros and cons of the client-server model ?

A

Pros

  • The data is backed up
  • The files and resources are centralized, controlled and monitored.
  • There is a high level of security (access rights)

Cons

  • It is complex to monitor
  • If the server fails all the users are affected
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7
Q

What is a peer-to-peer model ?

A

In the peer-to-peer model, all the nodes are interconnected and they communicate with each other. There is no central server.

All the computer are of equal status and each computer provides access to resources and data.

The nodes can communicate and share resources and in this model each node is responsible for its own security.

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8
Q

When are peer-to-peer models used ?

A

A peer-to-peer model is used when,

  • There is a small user base
  • There is no need for strong security
  • The application is workstation based

For example,

  • Bus networks
  • Mesh networks
  • Skype or Whatsapp
  • A small business with 5 employees
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9
Q

What are the pros and cons of the peer-to-peer model ?

A

Pros

  • It is easy to set up
  • There is less data congestion
  • If one of the devices fails, it doesn’t affect the rest of them

Cons

  • There is weak data security, each computer is at risk of malware from the others
  • There is no centralized data back-up so data can be lost
  • Since various systems have access to one computer there is a chance of malpractice
  • It is difficult to monitor and oversee user activity.
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10
Q

What is a thin client ?

A

A thin client is a device or software which is heavily dependent on having access to a server. The thin client will not work unless it is connected to a server at all times.

The server does all of the processing while the thin client simply sends the request and displays the result to the user.

The data is stored on a remote server

For example : - A web browser

It is an example of a peer-to-peer model

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11
Q

What is a thick client ?

A

A thick client is a device or software that can work offline or online. It can perform some processing whether or not it is connected to a server

The server performs some processing for the client but most of the processing is done by the thick client itself.

The data is stored on a local resource like an HDD or an SSD.

For example : - A Laptop or a video game

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12
Q

What is bus network topology ?

A
  • There is a single central cable to which all the nodes are connected
  • Data only travel in one direction and only one device can transmit data at a time . (it is half duplex)
  • Terminators are placed at each end of the cable

It should be used when there is a small number of devices with light traffic.

E.g. : - A small company

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13
Q

What are the pros and cons of bus network topology ?

A

Pros

  • Even if one node fails, the rest of the network continues to work normally.
  • It is easy to expand
  • Requires little cabling
  • Cheaper

Cons

  • If the main cable fails, the whole network collapses.
  • The network does not work well under heavy loading as data collisions tend to occur.
  • The network has weak data security since the data packet passes through EVERY node.
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14
Q

What is star network topology ?

A
  • It uses a central switch which each node is connected to
  • The data is sent from the sender to the central switch
  • So the data is sent bi-directionally
  • The switch reads the packet and forwards it to the destination node only

It should be use when there is a large organization and there is a lot of data traffic.

E.g : - LAN
It is an example of a client-server model

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15
Q

What are the pros and cons of star network topology ?

A

Pros

  • There is a very low chance of data collisions occurring
  • It is more secure since the packets only travel to the destination node
  • It is easy to add nodes
  • If any of the connections is broken it only affects one node.

Cons

  • If the central switch fails then the whole network collapses
  • It is expensive to set up
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16
Q

What is mesh network topology ?

A
  • All the nodes are interconnected with each other
  • It uses routing logic to determine the shortest possible route to the destination node and sends it using the calculated path

E.g. : - A smart home system

It is an example of a peer-to-peer model

17
Q

What are the pros and cons of mesh network topology ?

A

Pros

  • It is easy to identify where faults have occurred
  • Any broken links don’t affect the other nodes
  • There is good data privacy and security as the packets travel along dedicated routes
  • The network is easy to expand

Cons

  • It requires a large amount of cabling
  • Which is expensive and time consuming
  • It is complex to set up and maintain
18
Q

What is hybrid network topology ?

What are its pros and cons ?

A

It is a mixture of two or more topologies.

E.g : - A home network which uses both Wifi and ethernet

Pros

  • It can handle large volumes of traffic
  • It is easy to identify where a fault has occurred
  • It is well suited for the creation of large networks

Cons

  • It is expensive and difficult to set up
  • It is complex to manage
19
Q

What is cloud computing ?

What are its pros and cons ?

A

It is accessing a service/file/software on a remote server.

Pros

  • The data stored on the cloud can be accessed from anywhere with Internet access
  • The data is automatically backed up by the provider
  • It is easy to increase storage capacity
  • It is easy to share documents
  • Multiple people can be working on the same document

Cons

  • The data can’t be accessed if there is no internet access
  • The data can’t be accessed if the server is down
  • It is reliant on the provider for back up and security
  • It can take a long time to upload/download the data
  • It can be expensive
20
Q

What is Public cloud ?

What is Private cloud ?

A

Public cloud is when the client and the cloud storage provider are two different entities. The computing services of the provider are available to anyone with the appropriate credentials.

Private cloud is when the client and the cloud storage provider are the same entity. The computing services offered are available to only select users and the system is dedicated to some organization.

an example of a private cloud would be what government agencies use.

21
Q

IMPORTANT THINGS TO REMEMBER (Chapter 2)

A
  • Twisted pair cables are the cheapest, slowest and suffer the most from external interference
  • Coaxial cables are more expensive, a lot faster and are affected less by external interference but they suffer the most from signal attenuation but they have the anti-jamming properties.
  • Fiber optic cables are used to send data over long distances by transmitting data as light and using the concept of total internal reflection.

Fiber optic cables are the most expensive, fastest and have a high resistance to external interference and have the least signal attenuation.

22
Q

How is data transmitted using Radio waves ?

A

It carries data wirelessly in the form of EM waves

Pros

  • It can travel over large distances with a wide range of wavelengths
  • It is cheap
  • Used for mobile phone communications

Cons

  • It transmits less data at a time
  • Interference is caused by other radio stations with similar frequencies
23
Q

How is data transmitted using Microwaves ?

A

It also carries data wirelessly in the form of EM waves.

Pros

  • It has a larger range so allows for more data transfer

Cons

  • It is expensive to build emitting towers
  • Physical obstacles can interfere with the emitted signals
24
Q

How is data transmitted using satellites ?

A

The EM radiation from an antenna is beamed onto a satellite who boosts the signal and sends it to another antenna.

Pros

  • It has a large range of wavelengths
  • It allows access in remote areas
  • The connection is not fixed to a single location

Cons

  • There is lag
  • Slow data transfer speeds
  • It is expensive
  • Signal is affected by the weather

It is used for radio broadcasts and satellite phones

25
Q

What is a bridge ?

A

A bridge is a device that connects one LAN to another LAN that uses the same protocols.

It stores the network addresses for all the devices in the two networks and looks for the receiving address before it sends a message.

26
Q

What is a modem ?

A

A modulator demodulator, it allows a device to connect to the internet via a telephone line.

A transmitter uses a modem to convert digital signals to analogue signals and send them down the telephone line, on the other end a receiver also uses a modem to convert the analogue signals to digital signals to interpret the data.

27
Q

What is a Wireless Access point ?

A

It is a hardware component that is usually built into the router which allows a device to connect to the LAN via wifi instead of using a cable by providing radio communication from the central device to nodes on the network (and vice versa)

28
Q

What is the router ?

A
  • The router receives packets from devices
  • It finds the destination IP address of the packets
  • It calculates the most efficient path to the destination using the routing table it maintains
  • It forwards the packet to its destination using the calculated path
  • It acts as a gateway
  • It acts as a firewall
  • It assigns private IP addresses to devices on a LAN
  • It maintains a table of MAC and IP addresses
29
Q

What is the Network Interface Card ?

A
  • It provides each device in a wired LAN with a unique MAC address to uniquely identify it on the network
  • It allows each individual device to connect to the network
30
Q

What is a wireless network interface card ?

A
  • It provides each device in the wireless LAN with a unique MAC address to uniquely identify it on the network
  • It allows each individual device to connect to the network wirelessly instead of a cable

How it works

  • It provides an interface to the wireless network as an antenna.
  • It receives analog radio waves and converts them to a digital format
  • It checks the incoming transmissions for correct MAC address, ignores if not the devices MAC address.
  • It encrypts and decrypts the data
  • It converts the digital value to analogue waves
  • Emits the radio waves via the antenna
31
Q

What is ethernet ?

A

Ethernet is a protocol for data transmission over a cabled network

  • It uses CSMA/CD
  • The data is transmitted in frames, where each frame has a source and destination IP address and error checking data so any damaged frames can be resent
32
Q

What is CSMA/CD ?

A

Carrier sense multiple access with collision detection,

  • Listens to a channel and checks if its busy
  • If it is not busy then it transmits the data
  • Since there are more than one nodes in the system a collision may occur
  • If a collision occurs the transmission is aborted
  • Both nodes wait till a random amount of time elapses before they transmit again
33
Q

What is bit streaming ?

A

It is a sequence of digital bits being transferred over a communication path at high speeds, it requires a high broadband connection and buffers.

There are two types : -

Real time : - Live events captured and transmitted directly like a twitch stream

On-demand : - Pre-existing files are converted and streamed as requested.

34
Q

What are the differences between the world wide web and the internet ?

A

The WWW is a collection of interlinked multimedia webpages. it uses the internet to access information from servers.
The internet is the global connection of interconnected computer networks
The internet uses TCP/IP whereas the WWW uses http protocol.

Internet is transmitted using wired, radio or satellite.

35
Q

What is the PSTN

A
  • The public switched telephone network consists of many different types of communication lines.
  • Data is transmitted in both directions at the same time
  • The communication passes through different switching centers
36
Q

What is a dedicated line ?

A

It is a telecommunication path between endpoints.
It is private and not shared with multiple users.

It allows continuous, uninterrupted access to the web and is able to carry phone calls as well.

It gives a faster connection with a more consistent transmission speed and better security

However, it is expensive to set up and maintain and a disruption in the line would leave no alternative

37
Q

What is a cell phone network ?

A

It is a wireless network spread over land areas divided into hexagonal cells which sends data to cell towers over mobile connection.

Each cell has at least one base station which uses a different frequency range to its neighboring stations.

Radio waves are usually used for this transmission and can be broadcast in all directions to allow mobile phones to communicate and access the internet via these base stations.

Computer science AS level theory (4 decks)

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